LUSE, LDEV, LUN

[Avinash Kumar]

sorry to sound so stupid, but can someone tell me the difference between these ? ;)

 

[Ganesan Sudalai]

LUSE - Group or Collection of LDEVs (In Enterprise Storage term) / LUNs (Mid-Range)

LDEV - Small logical unit of reqired size under the Raid Group / Parity Group(Used in Enterprise Storages)

LUN -  Logical Unit No ( Same as LDEV in Mid - Range)

 

Whereas in Enterprise this is called H-LUN (Host LUN), like one L-DEV or LUSE can be mapped thru single LUN.

 

--
Cheers

Ganesh

Whatever the mind can conceive and believe, the mind can achieve.
~ Dr. Napoleon Hill

http://poigaiblog.blogspot.com/

 

[Avinash Kumar]

So this is how I understand these terms like this now

 

You create a raid group first (btw, what you mean by parity group ? )

 

then you create LDEVs under the Raid groups.

 

then create LUSE as a collection or group of LDEVS  (LDEVS under the LUSE will be striped or concatenated ?)

 

LUNs are just the logical unit number that u use to map a LDEV or LUSE to hosts.

 

Kind regards...Avi
 

[Jay]

Whoever explains this, it would be great if you could give examples.....

 

cheers...Jayanth

 

 

On 12/24/06, Avinash Kumar <avinash....@gmail.com> wrote:

[mahesh ravindra]

Hi ,

This terminology are command in XP series and HDS
9980/USP series .

LDEV:

LDEV is the Internal representation of a Chunk of
storage . if you take HDS USP.

First thing we do is format the disks (
6D+2P,3D+1P)... USP only supports Raid level
(0+1,5,6).
into smaller slices called LDEV and Assign it LDEVID
and CU(control Unit) ... This has come from the
Mainframe Era .

So let us take ,if you have 72GB disks 10K and you
want to format it on Raid 0+1 of 13.56GB Slices

We created 10 LDEVS of 13.56GB and assign each one an
address CU:LDEVID ( 00:00,00:01.....)

USP supports 16384 (Luns ) CU --64 (Max) , LDEVID
(0---255) Max

LUSE :

When you combain this LDEV ,Let us take customer wants
27 GB disk and u have Ldevs of 13.56GB

you combine 2 LDEV to form a LUSE

00:00 + 00:01 ---> 00:00 ( 27GB ) Concat Device and it
takes the address of first LDEV, You can combine upto
36 devices.

LUN .

After you have noted your required LDEV/LUSE . You
need to create path for this ldev for access by
external Host .When you create a PATH for the LDEV you
assign a LUN number ( Which is for access to External
Host ).

I guess this is clear ...If you not Please let me know
.

Thanks
Mahesh

--- Jay <jaya...@gmail.com> wrote:

> --
> What Ever !!!
>
>
>
>

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[Avinash Kumar]

Hi

 

having said that, is there any best practices when you define the size of LDEVs ?. And like you said, since LUSE concatenates the LDEVs your grouping, do you think it would be a good idea to map the LDEVs to lun and do the striping at the host side to gain the performance that could be affected otherwise ?

 

Kind regards...Avi

[Ganesan Sudalai]

Avinash,

 

Designing LDEV(LUN)s is an separate subect by itself :). What happens generally is that they make 2 kind of LDEV Sizes across the storage. Because its easier to create 1000s of LUNs and also its useful for Insystem and Remote Replication. Like they make it one small size and One Big Size. Later they export(Expose) the LUN to the hosts either as a single LDEV volume or LUSE (Combination of LDEVs) (Most of the Time). Like you can use Smaller LDEVs for Archive Logs and applications which uses the smaller volume sizes and Bigger LDEVs(LUSEs) for Data files and Fle servers in a typical storage environment.

 

When we talk about LUSE, its a concatenation of LDEVs and there is a performance problem if you combine LUNs from only the Same Raid Group(Parity Group). But you can also combine ONE Single LUSE using Multiple RaidGroup LDEVs and in this case single LUSE volume will have more no of Spindles for the End performance. So its the matter of how you define the LUSEs.

 

In case if you want to Export(Map) LDEVs to the Host systems and wanna stripe the LDEVs there, it requires Lot of CPU and other resources and Host side Striping / Raid conf is more prone to failure than Making LUSEs (RAID) in the Storage as it is specialised to do that job instead of Host operating system as it is designed for other purposes. Still you have some environments running this kind of Configurations.

 

At the End of the Day, you have to design with the given resources, Environment and required output with your best of the Knowledge :)

Hope this clarifies lil more and Feel free to write back in case of Any Doubt.

 

 

By the way, Looks like you are taking Online Class and Your Bill is on the way ;)

--
Cheers

Ganesh

Whatever the mind can conceive and believe, the mind can achieve.
~ Dr. Napoleon Hill

http://poigaiblog.blogspot.com/

 

[Jay]

Super....thanks Mahesh & Ganesan

 

A wonderful new year to all.....have fun

 

cheers....Jay

 

 

On 12/25/06, mahesh ravindra <maheshr...@yahoo.com> wrote:

--
What Ever !!!